The current invention relates to seat belt retractors.
A conventional seat belt retractor allows a vehicle occupant some freedom of movement, but has a sensor to detect acceleration above a predetermined magnitude indicative of an emergency situation. The seat belt retractor then locks, arresting the vehicle occupant""s movement. This can also occur when the vehicle occupant leans forward too quickly to reach a control on the instrument panel. Seat belts which allow movement are desirable for adult vehicle occupants as they restrain passengers in emergency situations but are comfortable because they allow a reasonable degree of freedom for movement during normal driving conditions. When transporting a young child with a child seat the child seat must be fixed in place, but it is desirable for the same seat belt retractor to also operate as a normal inertial retractor to provide the expected comfort for an adult.
This problem is a well known and several solutions have been proposed. U.S. Pat. No. 6,109,556 teaches a seat belt arrangement for motor vehicles, specially adapted for use with a child seat to switch between a fixed mode for the child seat and an automatic mode for adults. Such a seat belt retractor is known as a Child Hold Out Mechanism, sometimes referred to as a xe2x80x9cCHOMxe2x80x9d.
U.S. Pat. No. 6,109,556 teaches a retractor switching means comprising a cam connected to a spool via a step down gearing arrangement and a cam follower. The step down gearing arrangement comprises an inner gear ring and a gear arrangement with a drive peg located at a predetermined radius. The drive peg is arranged to move cycloidally and rotate the cam when the gear rotates. This cycloidal motion often results in the gear arrangement being known as a xe2x80x9cwobblexe2x80x9d gear. The cam follower is pivotally mounted and arranged to be in continuous contact with the cam surface. At a predetermined rotational orientation of the cam, the cam follower urges the sensor lever into engagement with a toothed ratchet wheel fixed to the spool to lock the spool and seat belt webbing protraction.
A particular problem with Child Hold Out Mechanism retractors is that a large number of components are needed and this increases the size of the retractor.
There is provided in accordance with the present invention a seat belt retractor comprising a spool for carrying seat belt webbing rotatably mounted about a longitudinal axis and biased in a seat belt webbing rewinding direction, a toothed ratchet wheel mounted to rotate with the spool, a sensor for detecting an emergency condition, a vehicle acceleration sensor lever responsive to the sensor to engage the ratchet wheel in the event of an emergency condition, means for locking the spool against pay-out of seat belt webbing in response to the vehicle acceleration sensor lever engaging the ratchet wheel, the retractor being adapted to operate in a first, emergency locking mode in which the spool is not locked and can rotate to pay-out and to rewind seat belt webbing. In a second, automatic locking mode in which the spool is locked against pay-out of the seat belt webbing and means for switching between the first mode and the second mode, wherein, the switching means comprises a cam connected to the spool via a step-down gearing arrangement and having a cam surface and an actuating lever having a cam follower resiliently biased against the cam surface, the actuating lever being pivotally mounted and moveable from a first position in which it does not actuate the vehicle acceleration sensor lever and the retractor is in the first mode against the action of the resilient bias to a second position in which it actuates the vehicle acceleration sensor lever and the retractor is in the second mode.